Some of my Mystbooks have taken to a habit of dropping me inside of a loaded chunk, and by inside, I mean inside the blocks present in that chunk. That includes lava.

Oddly, I have not (yet) suffered any damage or loss as a result, but please keep all appendages tightly clenched around your pick while on your travels. PSA brought to you by Miners' Anonymous: Admitting you hoard is the first block.